Method of splitting non-metallic brittle materials and devices for carrying out suchmethods



23, 1965 T. R. SELDENRATH ETAL 3,219,230

METHOD OF SPLITTING NON-METALLIC BRITTLE MATERIALS AND DEVICES FOR CARRYING OUT SUCH METHODS Filed Oct. 17, 1962 2 Sheets-Sheet l INVENTOR THEODORUS R. DENRATH JAN VERS TRAT FRANGISGUS J. H. TIMMERMANS BY}; 4 A

AGENT N 23, 1955 T. R. SELDENRATH ETAL 3,219,280

METHOD OF SPLITTING NON-METALLIC BRITTLE MATERIALS AND DEVICES FOR CARRYING OUT SUCH METHODS Filed Oct. 17, 1962 2 Sheets-Sheet 2 INVENTOR THEODORUS R. SELDENRATH JAN VERSTRATEN FRANGISOUS J. H. TIMFRMAN? AGENT United States Patent METHGD G13 SPLITTING NON-METALLIC BRITTLE MATERIALS AND DEVICES FOR CARRYING GUT SUCH METHODS Theodorus Regnerus Seldenrath, Rijswijk, and .Ian Verstraten and Franciscus Josephus Hendricus Timmermans, Einmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc, New York, N.Y., a corporation of Delaware Filed Oct. 17, 1%2, Ser. No. 231,123 Claims priority, application Netherlands, Oct. 30, 1961, 270,818 18 Claims. (Cl. 2411) This invention relates to methods of splitting nonmetallic brittle materials and devices for carrying out such methods, more particularly, for use in splitting stones in mine shafts, tunnels and the like.

An object of the invention is to provide a new concept for splitting such materials, which is distinguished inter alia by its particularly high effectiveness.

According to the invention, a radiating device designed as an injector is inserted into an inlet aperture recessed in the material to be split. The device is supplied with ultra high-frequency oscillations in the decimeter or centimeter range and is arranged to locally concentrate these ultrahigh-frequency oscillations in the interior of the material to be split at the area of the injector, said oscillations causing splitting of the material due to local internal dielectric heating thereof.

According to the invention, a device for carrying out this method comprises a radiating element in the form of an injector comprising two relatively perpendicularly polarized radiators each radiating substantially into the same local space. The device also includes two ultrahigh-frequency generators having output circuits which are coupled to a wave-guide system leading to the radiating element and feeding the two relatively perpendicularly polarized radiators. The device is arranged so that the ultrahigh-frequency generators are not coupled together.

In order that the invention may readily be carried into eifect, it will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows a device serving to explain the method according to the invention;

FIGS. 2 and 3 show a few particularly advantageous devices according to the invention for carrying out the method to be described with reference to FIG. 1, and

FIGS. 4 and 5 show, on a larger scale, a cross-section and longitudinal section of a component part in the device of FIG. 3.

In FIG. 1, the reference numeral 1 indicates a stone to be split and weighing, for example, several tons, in which a hole 2 is drilled. The hole 2 is made visible in the figure by removing part of the Wall of the stone. The drilled hole may be, for example, from 4 to 6 cms. in diameter, and its depth is from cms. to cms.

For splitting the stone, at radiating device 3 formed as an injector, is supplied through a wave-guide system 5 with ultrahigh-frequency oscillations provided by an ultrahigh-frequency generator 4, for example, of a wavelength of 12 cms. (2,450 mc./s.) and a power of 10 kilowatts. The injector is introduced into the drilled hole 2 for locally concentrating the ultrahigh-frequency oscillations in the interior of the stone 1 at the area of the injector 3 so that within a few minutes after switching on the ultrahigh-frequency generator 4, the stone 1 breaks into smaller pieces according to several split faces surrounding the hole 2.

In fact, the ultra-high frequency oscillations cause a strong local dielectric heating in the interior of the stone 1 around the drilled hole 2, resulting in exceptionally high internal tensions being produced in the interior of the stone 1 causing it to fall to pieces within a few minutes.

Apart from the particularly effective action of this novel concept for splitting stones, in which the properties of the stone are utilized in an elegant way, this new concept is further distinguished in that the splitting process takes places without any appreciable development of dust, which is very important for the health of the operating staff. This splitting method is particularly eifective for very hard stones which are difficult to split in any other way as, for example, granite.

FIGS. 2 and 3 show two particularly advantageous devices according to the invention for carrying out the method described hereinbefore. In order to obtain optimum conditions, these devices are designed so that in each case the power concentration of the ultrahighfrequency oscillations is a maximum at the area of the radiating device formed as an injector. In fact, extensive tests have revealed that the splitting process increases progressively with the power concentration of the ultrahigh-frequency radiation emitted by the radiating device.

A device for carrying out the above-described method is shown in perspective in FIG. 2 and comprises two magnetron generators 7, 8 which are connected through coaxial lines 9, 1G to a wave guide 11. Waveguide 11 guides the ultrahigh-frequency oscillations, for example, of a wavelength of 12 cms. 2,450 mc./s.), produced by the two magnetron generators 7, 8 to a radiating device 12 formed as an injector. The injector may be placed in the hole 2 of 5 cms. in diameter drilled in the stone 1 to be split. The two magnetron generators 7, 8 employed may be of a type which provides a maximum power of 5 kilowatts.

In the device shown, the two magnetron generators 7, 8 are coupled to the Wave guide 11 by means of the inner conductors 13, 14 of the coaxial lines 9, 10. Conductors 13, 14 are inserted perpendicularly to each other into the wave guide 11, each of the relatively perpendicular inner conductors 13, 14 radiating a linearly-polarized electromagnetic field having a direction of polarization parallel to the relevant inner conductor 13 or 14. The two electromagnetic fields having relatively perpendicular directions of polarization are supplied, without the magnetrons 7, 8 directly acting upon each other, to the radiating device 12, formed as an injector, through the wave guide 11 which, in order to permit its connection to the radiating device 12 having a diameter less than 5 cms., gradually narrows in the axial direction, for example, from a diameter of 10 cms. to the diameter of the radiating device 12.

Where the narrowing of the wave guide 11 begins, two pairs of diametrically opposite guide strips 15, 16 are provided on the inner wall thereof in directions parallel to the directions of polarization of the two emitted electromagnetic fields. The field of the magnetron 7 has a direction of polarization parallel to the conductive strips 15 and propagates substantially in the narrow gap between the two conductive strips 15 in the axial direction. In a similar manner the field of the other magnetron 8 is guided in the axial direction through the gap between the two other conductive strips 16. Unhindered by the narrowed portion of the wave guide 11, the two relatively perpendicularly polarized fields of the magnetrons 7, 8 propagate in the gaps between the diametrically opposite conductive strips 15, 16. The conductive strips 15, 16 also extend outside the wave guide 11 thereby forming two relatively perpendicularly polarized radiators constituting together the radiating device 12 formed as an injector. More particularly, the gap located between the conductive strips 15 forms a gap radiator for the oscilla tions from the magnetron 7. The gap between the conductive strips 16 forms a gap radiator for the oscillations from the magnetron 8 which are polarized at right angles to the first mentioned oscillations. The electromagnetic fields thus radiated cause strong dielectric heating of the stone mass 1 surrounding the drilled hole 2. Any surface currents flowing at the outer periphery of wave guide 11 adjacent the radiating device 12 are damped by the surrounding stone mass 1. Apart from the oscillations produced by the magnetrons 7, 8 being radiated into the same local space without the magnetrons 7, 8 interacting with each other, each of the magnetron 7, 8 may be matched to the load formed by the stone 1 independently of each other, that is to say an optimum transmission of power to the load may be obtained for each of the magnetrons 7, 8.

In the device shown, the magnetron 8 is matched to the load by adjusting the depth of insertion of the inner conductor 14 of the coaxial line 10 and displacing a tuning piston 17. The magnetron 7 is matched by adjusting the depth of insertion of the inner conductor 13 of the coaxial line 9 and displacing a polarizing grid 18 positioned between the inner conductors 13, 14. The grid passes the oscillations from the magnetron 8 and reflects the oscillations from the magnetron 7. In the device shown, in which the length of the radiating device 12 is about \=9 cms., it has been found advantageous for favourable matching to short-circuit the conductive strips 15, 16 by means of a short-circuit piece 19.

This device not only permits a maximum power concentration at the radiating device 12 formed as an injector, so that a particularly effective splitting process is realized, as explained hereinbefore, but also the relatively perpendicular directions of polarization of the two radiated electromagnetic fields are particularly advantageous for this splitting process. In fact, from tests carried out especially with stratified stones, the splitting process has been found to be dependent upon the direction of polarization of the radiated electromagnetic field and has been found, for example, to show a minimum for a given direction of polarization and a maximum for a direction of polarization approximately at right angles thereto. By simultaneously radiating two electromagnetic fields having relatively perpendicular directions of polarization, an effective splitting action is thus insured irrespective of the structure of the stone.

FIG. 3 is a perspective view of another embodiment of a device according to the invention in which all the advantages of the device of FIG. 2 are also realized.

As in the device of FIG. 2, the device shown in FIG. 3 comprises two magnetrons '7, 8 each of kilowatts, designed to produce oscillations of a wave-length of 12 cms. (2,450 mc./s.). Coaxial lines 9, are connected to the output circuits of the magnetrons 7, 8 for coupling them to a wave-guide system which guides the oscillations produced by the magnetrons 7, 8 to a radiating device 20 in the form of an injector comprising two perpendicularly-polarized radiators.

In contrast to the device shown in FIG. 2, the waveguide system now comprises two concentric coaxial lines. The magnetron 7 is connected to the inner coaxial line comprising conductors 21, 22 and the magnetron 8 is connected to the outer coaxial line comprising conductors 22, 23 in order to feed separately the two relatively perpendicularly polarized radiators. More particularly, the magnetron 8 feeds through the coaxial line 22, 23 a linear radiator 24, for example, having a length of 6 cms., formed by the inner conductor 22 of coaxial line 22, 23 led to the exterior. The magnetron 7 feeds through the coaxial line 21, 22 an annular radiator 25 placed on the inner conductor 22 of coaxial line 22, 23 formed as the linear radiator 24.

To illustrate clearly the construction of the annular radiator 25, FIGS. 4 and 5 show a cross-section and a longitudinal section thereof on a larger scale. As may be seen from these figures, the annular radiator 25 comprises a plurality, for example, four spaced coaxial segments 26, 27, 28, 29 of a ring. The segments are energized through radially-directed coaxial pieces of line 30, 31, 32, 33 by the inner conductor 21 of coaxial line 21, 22 so that in each case the inner conductor of a coaxial segment 26, 27, 28, 29 is connected to the outer conductor of a subsequent segment 27, 28, 29, 26, for example, by making the relevant part of each segment 27, 28, 29, 26 of solid metal, as indicated by cross-hatching. All the segments 26, 27, 28, 29 of the annular radiator 25 are then excited with equal phase, resulting in circular currents of equal direction, as indicated by arrows, flowing in the outer conductors of the segments 26, 27, 28, 29 provided that these outer conductors have a length smaller than a half wave-length of the oscillations produced. For example, the segments 26, 27, 28, 29 in the embodiment shown each have a length of 4 cms.

In the device shown in FIG. 3, as in that of FIG. 2, two perpendicularly polarized electromagnetic fields are radiated into the same local space. The direction of the axial current in the linear radiator 24 is exactly at right angles to the direction of the circular current in the annular radiator 25, and in addition interaction of the magnetrons 7, 8 is also substantially avoided.

The magnetron 8, which is connected to the linear radiator 24, may be matched to the load by suitable choice of the length of the linear radiator 24 and by means of a displaceable tuning piston 34 provided on the end of coaxial line 22, 23 remote from the annular radiator 25. The magnetron 7, which is connected to the annular radiator 25 may be matched to the load by means of tuning pistons 35, 36 displaceable respectively towards the extremity of the linear radiator 24 and the other extremity of coaxial line 21, 22. As in the device shown in FIG. 2, optimum transmission of energy from the magnetrons 7, 8 to the load formed by the stone is thus ensured.

In this way, the device of FIG. 3 has, as previously mentioned, all the advantages of the device of FIG. 2. Characteristic of these devices is that the radiating device formed as an injector comprises two relatively perpendicularly polarized radiators each radiating substantially into the same local space and two ultrahigh-frequency generators have output circuits which are coupled to a wave-guide system leading to the radiating device and feeding the two relatively perpendicularly polarized radiators, the ultrahigh-frequency generators not being coupled together.

In conclusion, it is to be noted that in order to avoid damage in introducing the radiating device 12, 20 formed as an injector into the hole 2 drilled in the stone 1, it is advantageous for the said device to be protected by means of a protective cap made from a material substantially free from dielectric losses, for example, polytetrafluorthylene.

What is claimed is:

1. Apparatus for fracturing a body of non-metallic brittle material, comprising means for generating high frequency electromagnetic wave energy, and means for radiating said wave energy into a localized area within a recess in said body, said latter means comprising a nonradiating electromagnetic wave transmission system having one end thereof insertable in said recess and wave energy radiating means disposed at the said end of said transmission system, said wave energy radiating means being formed as an injector for concentrating the radiated electromagnetic energy within said recess, and means for coupling said wave energy generating means to said transmission system at a point thereof spaced from the said end.

2. Apparatus for fracturing a body of non-metallic brittle material, comprising first and second sources of high frequency electric energy, means for radiating said high frequency energy into a localized area within a recess in said body, said radiating means comprising waveguide means having one end thereof insertable in said recess and including wave energy radiating means disposed at the said end of said Waveguide means, said Wave energy radiating means comprising an injector having first and second conductive elements extending from said one end of said waveguide means, and means for coupling said first and second energy sources to said waveguide means at a point thereof spaced from the said end, said Waveguide means further comprising means for individually coupling the high frequency energy from said first and second sources to said first and second conductive elements, respectively.

3. Apparatus for fracturing a body of non-metallic brittle material having a recess therein comprising, means producing first and second waves of high frequency electromagnetic energy, energy radiating means in the form of an injector comprising first and second radiating elements which are arranged to radiate two mutually orthogonal polarized electromagnetic waves into the recess in said body, Waveguide means coupled to said radiating means, and first and second substantially decoupled means for introducing said first and second waves of electromagnetic energy into said waveguide means whereby said first and second waves are coupled to said first and second radiating elements, respectively.

4. Apparatus for fracturing a body of non-metallic brittle material having a recess therein comprisnig, first and second means for generating high frequency electric oscillations, energy radiating means in the form of an injector comprising first and second radiating elements which are arranged to radiate two mutually orthogonal polarized electromagnetic waves into the recess in said body, waveguide means coupled to said radiating means, first and second coupling means for coupling said first and second generating means, respectively, to said waveguide means, said first and second coupling means comprising means for radiating first and second linearly polarized electromagnetic waves having mutually orthogonal directions of polarization into said waveguide means, said waveguide means being tapered inwardly towards said injector and including means to guide said first and second orthogonal waves to said first and second radiating elements, respectively.

5. Apparatus as described in claim 4 wherein said first and second coupling means comprises first and second coaxial lines, respectively, having their respective inner conductors extending into said waveguide means in mutually perpendicular directions.

6. Apparatus for fracturing a body of non-metallic brittle material comprising, first and second means for generating high frequency electric oscillations, energy radiating means in the form of an injector comprising first and second radiating elements which are arranged to radiate two mutually othrogonal polarized electro-magnetic waves, waveguide means coupled to said radiating means, first and second coupling means for coupling said first and second generating means, respectively, to said waveguide means, said first and second coupling means comprising first and second conductive elements, respectively, extending into said waveguide means in mutually perpendicular directions thereby to radiate first and second linearly polarized electromagnetic waves having mutually orthogonal directions of polarization, said waveguide means being tapered inwardly towards said injector thereby to guide said first and second orthogonal waves to said first and second radiating elements, respectively.

7. Apparatus as described in claim 6 wherein said wave guide means comprises a first pair of diametrically opposed conductive strips which extend in a direction parallel to the direction of polarization of said first linearly polarized wave and a second pair of diametrically opposed conductive strips which extend in a direction parallel to the direction of polarization of said second lineary poarized wave, said first and second pairs of conductive strips being mounted in the tapered portion of said Wave guide on the inner wall thereof and extending beyond the end of said waveguide to form two relatively perpendicularly polarized radiating elements.

8. Apparatus as described in claim 7 wherein said first and second conductive elements are spaced apart in the longitudinal direction of said Waveguide and further comprising means for matching at least one of said first and second high frequency generating means to the load comprising the body to be fractured, said load matching means comprising a plate having a plurality of grid-like apertures therein and mounted within said waveguide between said first and second conductive elements and oriented to transmit the linearly polarized wave radiated from the conductive element furthest removed from said energy radiating means and which reflects the linearly polarized wave from the other conductive element.

9. Apparatus as described in claim 7 further comprising a conductive member connected across said conductive strips at the forward exposed end thereof thereby to provide a short circuit connection between said strips.

10. Apparatus as described in claim 7 further comprising a tubular cap enclosing the exposed end of said conductive strips and composed of a material having low dielectric losses.

11. Apparatus as described in claim 7 wherein the exposed ends of said conductive strips extend approximately /1 A outside of said waveguide, wherein A is the wavelength of the high frequency oscillations generated.

12. Apparatus for fracturing a non-metallic brittle material comprising, first and second sources of high frequency electric oscillations, and means for radiating high frequency electromagnetic wave energy into a localized area, said radiating means comprising a pair of concentric coaxial lines, the inner conductor of the outer coaxial line extending beyond the end of the outer conductor of said outer coaxial line to form a linear radiating element, an annular radiating element coaxially mounted about said linear radiating element and electrically connected to the inner coaxial line, and means coupling said first highfrequency source to one of said coaxial lines and said second source to the other of said pair of coaxial lines whereby two mutually orthogonal electromagnetic waves are radiated from said linear and annular radiating elements into said localized area.

13. Apparatus as described in claim 12 wherein said annular radiating element comprises a plurality of spaced coaxial segments forming a ring surrounding said linear radiating element, a plurality of radially-extending coaxial conductor members connecting each of said coaxial segments to the inner conductor of said inner coaxial line, each of said conductor members including means for electrically connecting the inner conductive surface of a coaxial segment to the outer conductive surface of the next adjacent coaxial segment.

14. Apparatus as described in claim 13 wherein the length of the outer surface of each of said coaxial segments is less than one half wavelength of said high frequency oscillations.

15. Apparatus as described in claim 12 wherein said annular element is mounted inwardly from the radiating end of said linear radiating element and further comprising a conductive disc coaxially mounted about the inner conductor of the inner coaxial line and axially displaceable between said annular element and the forward end of said linear radiating element.

16. A device for fracturing a body of non-metallic brittle material comprising, a radiator of high frequency electromagentic energy in the form of an injector, first and second sources of high frequency electric energy, a pair of concentric coaxial lines comprising an inner conductor, an outer conductor, and an intermediate conductor coaxially aligned, the inner coaxial line comprising said inner and said intermediate conductors and the outer coaxial line comprising said intermediate and said outer conductors,

means electrically connecting said first high frequency source to said inner coaxial line and said second high frequency source to said outer coaxial line, said intermediate conductor extending beyond the forward end of said outer conductor to form a linear radiating element which carries an axial current therein, a ring shaped radiating element coaxially mounted on said linear element and divided into a plurality of circumferentially spaced conductor segments, each of said segments having a solid portion and a hollow portion forming an inner and an outer conductor, a plurality of radially extending coaxial lines, one for each ring segment, each of said radial coaxial lines comprising an inner conductor connecting said solid portion of polarized electromagnetic fields which are radiated into the surrounding area.

17. The method of fracturing non-metallic brittle materials comprising the steps of forming a recess in said materials and radiating two high frequency linearly polarized electromagnetic fields having mutually orthogonal directions of polarization into said recess.

18. The method of fracturing non-metallic brittle materials by means of a radiating device in the form of an injector comprising the steps of producing first and second high frequency electric oscillations, supplying said first and second high frequency oscillations to said radiating device whereby two mutually orthogonal linearly polarized electromagnetic fields are radiated therefrom, and inserting said injector radiating device into a recess in said material thereby to fracture said material by the stresses produced due to local internal dielectric heating thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,308,860 1/ 1943 Clark 299--14 2,605,383 7/1952 Spencer 21910.55 2,859,952 11/1958 La Tour et al 241-1 FOREIGN PATENTS 140,773 1/ 1961 Russia.

OTHER REFERENCES The Coal Commentator, Far out Mining, Coal Age, April 1961, page 11.

Kravchenko et al.: Dustless Breaking of Rocks Electrically, Mining Congress Journal, May 1961, pages 53-55.

ANDREW R. JUHASZ, Primary Examiner.

J. SPENCER OVERHOLSER, Examiner. 

1. APPARATUS FOR FRACTURING A BODY OF NON-METALLIC BRITTLE MATERIAL, COMPRISING MEANS FOR GENERATING HIGH FREQUENCY ELECTROMAGNETIC WAVE ENERGY, AND MEANS FOR RADIATING SAID WAVE ENERGY INTO A LOCALIZED AREA WITHIN A RECESS IN SAID BODY, SAID LATTER MEANS COMPRISING A NONRADIATING ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM HAVING ONE END THEREOF INSERTABLE IN SAID RECESS AND WAVE ENERGY RADIATING MEANS DISPOSED AT THE SAID END OF SAID TRANSMISSION SYSTEM, SAID WAVE ENERGY RADIATING MEANS 